The present invention generally relates to lubricant compositions and more specifically to a lubricant composition containing an additive that is useful in reducing both silver wear and copper corrosion.
Large numbers of medium speed diesel engines in the United States, as well as other countries, utilize silver-plated bearings. Apart from providing stability against oxidation and protection against the formation of sludge and carbonaceous deposits, crankcase lubricating oils intended for use in medium speed diesel engines must also be formulated with specialized silver protective agents in order that silver parts in the engine are not attacked either by the additives in the oil or by the dispersed neutralized decomposition products produced during extended engine operation. Such agents, often referred to as silver lubricity agents or silver-wear additives, protect against extreme pressure, wear and corrosion.
It is well known that zinc-containing wear agents such as zinc dihydrocarbyldithiophosphates (typically used in passenger cars) are incompatible with silver bearings and cannot be used for this purpose.
The antagonism between zinc-containing wear inhibitors and the silver parts in diesel engines has been circumvented in the prior art by using alternative silver lubricity agents, the most common of which are the chlorinated hydrocarbons. However, while the chlorine compounds of the prior art have been shown to be effective in protecting the silver parts of diesel engines, the Occupational Safety and Health Administration in the United States and other public health agencies throughout the world have expressed concern over potential biological effects of chlorinated compounds. Therefore, an incentive exists to develop novel compositions effective in protecting the silver parts of medium speed diesel engines which overcome the problems or potential problems encountered with the zinc-containing and chlorine-containing wear inhibitors.
A related problem in obtaining silver protection in lubricant compositions is that many of the heavy-duty diesel engines also contain copper-moving parts. It is believed that corrosive oils oxidize the copper and bring the copper residue into the oil. The copper residue catalyzes further oxidation which results in increased oil viscosity and premature oil additive failure. Accordingly, it is desirable that a lubricating oil inhibit copper corrosion and subsequent oil failure.
Therefore, a need exists for diesel lubricant compositions that will not only protect the silver parts of the diesel engine, but also operate so as to inhibit copper corrosion. It is particularly advantageous to provide a single additive that will afford both silver-wear protection and copper-corrosion protection.
Hutchison (U.S. Pat. No. 4,871,465) discloses lubricant compositions in which silver protection is afforded by a combination of an organo-sulfur compound and hydrocarbon-substituted 1,2,4-triazoles, the latter being obtained by reaction of a dicarboxylic acid compound, such as polybutyl-succinic anhydride, with a guanidine derivative (column 4, line 56 to column 5, line 3). In other words, Hutchison discloses a triazole formed from a dicarboxylic acid and guanidine. The likely structure of this reaction product is the bis-triazole having two five-membered heterocyclic rings, as illustrated at column 7, lines 33-39.
Hutchison (U.S. Pat. No. 4,948,523) discloses a silver protective lubricant composition including a silver protective agent comprising the reaction product of a C.sub.5 to C.sub.60 aliphatic carboxylic acid and at least one amine selected from the group consisting of
(1) guanidine, urea, and thiourea compounds; PA1 (2) C.sub.1 to C.sub.20 hydrocarbyl mono-amines, alkylene diamines, and polyalkylene polyamines; and PA1 (3) N-alkyl glycine.
Schmid (E.P. No. 249,162) discloses the use of 3-amino-1,2,4-triazoles as corrosion inhibitors for nonferrous metals (i.e., copper or zinc). The 3-amino-1,2,4-triazole of the reference is derived from formic acid and amino guanidine hydrogen carbonate. Schmid does not disclose silver protection, much less copper corrosion protection in diesel railroad locomotives.
Lange et al. (U.S. Pat. No. 4,491,527) discloses ester-heterocycle compositions useful as "lead paint" inhibitors in lubricants. Lange et al. teaches a combination of esters of substituted carboxylic acids and heterocyclic condensation products of the substituted carboxylic acids containing at least one heterocyclic moiety.
Lange, et al. is not directed to a lubricant composition for use in diesel engines having silver parts. In fact, at column 12, an illustrative lubricant composition is shown to include a zinc dialkylphosphorodithioate wear inhibitor. As noted above, zinc is unacceptable for use in silver-containing diesel engines.
LeSuer et al. (U.S. Pat. No. 3,272,746) discloses a detergent composition wherein the disclosure teaches that a critical aspect of the invention is the size of the hydrocarbon substituent, requiring at least 50 aliphatic carbon atoms. Further, LeSuer discloses several nitrogen-containing groups. However, LeSuer does not recognize that the particular nitrogen containing hydrazine of my invention is advantageous whereas the ethylenediamine that LeSuer teaches is equivalent in his invention is detrimental in my invention (see Comparative Examples D and E of the present specification).
In view of the problems cited earlier, a general object of the present invention is to provide a silver-wear and copper-corrosion protection lubricant additive.
A further object of the invention is to provide a silver-wear and copper-corrosion protection lubricant additive composition suitable for addition to lubricant compositions used to lubricate the moving parts of medium speed diesel engines such as found in railway locomotives, marine towboats, and stationary power applications.